Osteonecrosis is a condition in which a decrease in the blood supply to bone results with the death of marrow and osteocytes and collaps of the necrotic segment. The femoral head is the most frequently affected site and the condition is bilateral in more than 60% of cases. Corticosteroids and excessive alcohol intake are major risk factors for the disease. Radiologic changes are typical at the late stages of the disease, but x-ray can be normal at early stages. Understanding the causes and pathogenesis aids early diagnosis which leads to more effective management. In the earlier stages, the goal is to retard disease progression and prevent femoral head collaps. In the later stages, after significant collaps has occurred, management is conservative until reconstructive surgery.